Multilayer printed circuit board and multilayer printed circuit board manufacturing method

ABSTRACT

A multilayer printed circuit board has an IC chip  20  included in a core substrate  30  in advance and a transition layer  38  provided on a pad  24  of the IC chip  20 . Due to this, it is possible to electronically connect the IC chip to the multilayer printed circuit board without using lead members and a sealing resin. Also, by providing the transition layer  38  made of copper on the die pad  24 , it is possible to prevent resin residues on the pad  24  and to improve connection characteristics between the pad  24  and a via hole  60  and reliability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 10/793,515filed Mar. 4, 2004, which is a continuation of U.S. application Ser. No.10/181,682, filed Jul. 17, 2002, now U.S. Pat. No. 6,909,054, issuedJun. 21, 2005, which is a National Stage, 35 USC 371, of Internationalpatent Application PCT/JP01/00177, filed Jan. 12, 2001, and further isbased upon and claims the benefit of priority from the prior JapanesePatent Applications No. 2000-152973, filed May 24, 2000, No.2000-105212, fled Apr. 6, 2000, No. 2000-078206, filed Mar. 21, 2000,No. 2000-073558, filed Mar. 16, 2000, and No. 2000-049121, filed Feb.25, 2000.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a buildup multilayer printed circuitboard and particularly relates to a multilayer printed circuit boardincluding electronic components such as an IC chip and a multilayerprinted circuit board manufacturing method.

BACKGROUND OF THE INVENTION

An IC chip is electrically connected to a printed circuit board by amounting method such as a wire bonding method, a TAB method or aflip-chip method.

In the wire bonding method, an IC chip is die-bonded to a printedcircuit board by adhesive or the like, the pads of the printed circuitboard are connected to the pads of the IC chip by wires such as metallicwires and then a sealing resin such as a thermosetting resin or athermoplastic resin is applied to protect the IC chip and the wire.

In the TAB method, wires referred to as leads are connected in the blockby a solder or the like and then the bumps of an IC chip and the pads ofa printed circuit board are sealed by a resin.

In the flip-chip method, the pads of an IC chip are connected to thepads of a printed circuit board by through bumps and the gaps betweenthe bumps and the respective pads are filled with a resin.

In each of these mounting methods, however, the IC chip and the printedcircuit board are electrically connected to each other through leadmembers (wires, leads or bumps) for connection therebetween. These leadmembers tend to be cut off and eroded, making the connection of theprinted circuit board to the IC chip cut off or causing malfunctions.

In addition, in each of these mounting methods, a sealing thermoplasticresin such as an epoxy resin is employed to protect the IC chip.However, if bubbles are contained at the time of filling the resin, thenthe lead members are broken, the IC pads are eroded and reliability ofthe IC chip is deteriorated due to the bubbles. To seal the IC chip orthe like by a thermoplastic resin, it is required to create resinfilling plungers and metallic molds in accordance with the respectivecomponents of the printed circuit board. Further, in case of employing athermosetting resin, it is necessary to select a thermosetting resin inview of the materials of the lead members, a solder resist and the like,thereby disadvantageously causing cost increase.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-stated problems.It is an object of the present invention to propose a multilayer printedcircuit board capable of being directly, electrically connected to an ICchip without using a lead member and a manufacturing method of themultilayer printed circuit board.

After being devoted to the intensive studies of the multilayer wiringboard, the inventors of the present invention finally devised astructure capable of electrically connecting a multilayer printedcircuit board to an IC chip without using leads and a sealing resin byproviding opening portions, through holes and counterbore portions inthe resin insulating substrate to thereby contain an electroniccomponent such as an IC chip therein in advance, building up a pluralityof interlayer insulating layers, providing via holes on the die pads ofthe IC chip by photoetching or laser, forming conductor circuits servingas conductive layers, and further providing the interlayer insulatinglayers and the conductive layers repeatedly to thereby provide themultilayer printed circuit board.

Moreover, the inventors of the present invention devised a structure ofmountino an electronic component, such as an IC chip, on the surfacelayer of the multilayer printed circuit board by providing openingportions, through holes and counterbore portions in the resin insulatingsubstrate to thereby contain an electronic component, such as an ICchip, therein in advance, building up interlayer insuiating layers,providing via holes on the die pads of the IC chip by photoetchinc orlaser, then forminc conductor circuits serving as conductive layers andfurther providing the interlayer insulating layers and the conductivelayers repeatedly. With this structure, it is possible to electricallyconnect the multilayer printed circuit board to the IC chip in withoutusing leads. It is also possible to mount the electronic components suchas the IC chip having different functions and to obtain a multilayerprinted circuit board having a greater function. To be specific, a cachememory is embedded as the IC chip included in the board and an IC chiphaving an operation function is mounted on the front surface of themultilayer printed circuit board, whereby it is possible to arrange theIC chip and the cache memory in proximity while separately manufacturingthe cache memory having low yield and the IC chip.

Furthermore, after being devoted to the intensive studies, the inventorof the present invention devised providing opening portions, throughholes and counterbore portions in resin insulating substrate to therebycontain an electronic component such as an IC chip in advance andforming a transition layer consisting of at least two-layer structure onthe die pad of the IC chip. An interlayer insulating layer is providedon the transition layer and a via hole is provided on a via hole whichis the transition layer of the IC chip by photo-etching or laser and aconductor circuit serving as a conductive layer. Thereafter, interlayerinsulating layers and conductive layers are repeatedly built up and amultilayer printed circuit board is provided, thereby making it possibleto electrically connect the multilayer printed circuit board to the ICchip without using a sealing resin and leads. Further, since thetransition layer is formed on the IC chip portion, the ICchip portion isflattened. Accordingly, the upper interlayer insulating layer isflattened and the thickness thereof becomes uniform. Further, thetransition layer makes it possible to maintain the stability of a shapein case of forming the via hole on the upper layer.

The reasons for providing the transition layer on the pad of the IC chipare as follows. First, if the die pad becomes fine pitch and small insize, alignment at the time of forming via holes becomes difficult. Dueto this, by providing a transition layer, the alignment is facilitated.If the transition layer is provided, buildup layers can be stably formedeven while a die pad pitch is 150 μm or less and a pad size is 20 μm orless. If the via hole is formed in the interlayer insulating layer withthe die pad on which the transition layer is not formed and the diameterof the via is larger than the diameter of the die pad, then a polyimidelayer serving as the protective layer of the surface of the die pad isdissolved and damaged at the time of removing the residue on the bottomof the via and roughening the surface of the interlayer resin insulatinglayer. On the other hand, if laser is applied and the via diameter islarger than the diameter of the die pad, a polyimide layer (orprotective layer of the IC) is damaged by the laser. Moreover, if thedie pad of the IC chip is very small and the diameter of the via islarger than the size of the die pad, then positioning becomes quitedifficult even by photo-etching or laser and connection errors occurbetween the die pad and the via hole.

By providing the transition layer on the die pad, by contrast, it ispossible to ensure connecting the via on the die pad even with a die padpitch of 150 μm or less and a pad size of 20 μm or less, therebyimproving the connection between the pad and the via and reliability. Inaddition, by interposing the transition layer having a larger diameteron the pad of the IC chip, the fear that the protective film of die padand the IC are dissolved and damaged if the protective film is immersedin an acid or an etching solution in later steps such as a de-smear andplating steps or conducting various annealing steps, is eliminated.

The multilayer printed circuit board itself fulfils the functions. Insome cases, BGA's, solder bumps or PGA's (conductive connection pins)may be provided to connect to a mother board or a daughter board whichis an external board so as to function as a package substrate for asemiconductor device. With this constitution, wiring length and loopinductance can be reduced compared with a case of connecting themultilayer wiring board to the external board by a conventional mountingmethod.

Now, the transition layer defined in the present invention will bedescribed.

The transition layer means a mediate layer provided on an intermediateportion so as to directly connect the IC chip, which is a semiconductorelement, to the printed circuit board without using a conventional ICchip mounting technique. The transition layer is characterized by beingformed out of two or more metallic layers or by being made larger thanthe die pad of the IC chip which is the semiconductor element. Thetransition layer thus characterized enables the enhancement ofelectrical connection and positioning characteristics and via holeprocessing by means of laser or photo-etching without damaging the diepad. This can ensure embedding and containing the IC chip in the printedcircuit board, and connecting the IC chip to the printed circuit board.This also enables a metallic layer serving as the conductive layer ofthe printed circuit board to be directly formed on the transition layer.For example, the conductive layer is the via hole of the interlayerresin insulating layer or a through hole on the substrate.

As a resin substrate for including electronic components such as the ICchip therein used in the present invention, a substrate obtained bybuilding up prepregs impregnated with a resin or a glass epoxy resinobtained by impregnating an epoxy resin, a BT resin, a phenol resin orthe like with a reinforcement or a core material such as a glass epoxyresin. An ordinary resin substrate used for the printed circuit boardmay be used. Alternatively, a double-sided copper-clad laminate, aone-sided plate, a resin plate without a metallic film or a resin filmmay be used. However, if the resin is heated at 350° C. or higher, theresin is dissolved and carbonated. Further, ceramic cannot be used forthe substrate since it is inferior in outside workability.

The IC chip is coupled to a resin insulating substrate such as a coresubstrate in which a cavity formed as a counterbore, a through hole oran opening for containing an electronic component such as the IC chip,by an adhesive or the like.

The entire surface of the core substrate including the IC chip issubjected to deposition, sputtering or the like, thereby forming aconductive metallic film (or first thin film layer) on the entiresurface. The metal used may be tin, chromium, titanium, nickel, zinc,cobalt, gold, copper or the like. The thickness of the conductivemetallic film is preferably between 0.001 and 2.0 μm. If the thicknessis smaller than 0.001 μm, the conductive metallic film cannot beprovided uniformly on the entire surface. It is difficult to form aconductive metallic film having a thickness exceeding 2.0 μm and even ifformed, the film does not improve advantages. The thickness is morepreferably between 0.01 and 1.0 μn. If chromium is used, the thicknessis preferably 0.1 μm.

The first thin film layer covers the die pad, thereby making it possibleto improve the adhesiveness of the transition layer and the IC chip toan interface with the die pad. Further, by covering the die pad withsuch a metal, it is possible to prevent the entry of moisture into theinterface, to prevent the dissolution and erosion of the die pad and toimprove reliability. In addition, the first thin film layer allows theconnection between the multilayer printed circuit board and the IC chipby a mounting method without using leads. If using chromium, nickel ortitanium, it is possible to prevent the entry of moisture into theinterface and excellent metal adhesiveness is ensured. The thickness ofchromium, titanium or the like is set so that the sputtered layer doesnot crack and that adhesiveness between the metal and the upper layer isensured. With a reference to a positioning mark on the IC chip, apositioning mark is formed on the core substrate.

The second thin film layer is formed on the first thin film layer bysputtering, deposition or electroless plating. The metal used isexemplified by nickel, copper, gold, silver or the like. It ispreferable to use copper because it has appropriate electricalcharacteristic and is economical and a thickening layer formed in alater step mainly consists of copper.

The reason for providing the second thin film layer is that only thefirst thin film layer cannot provide a electroplating lead to form athickening layer to be described later. The second thin film layer 36 isemployed as a thickening lead. The thickness of the second thin film ispreferably 0.01 to 5 μm. If the thickness is smaller than 0.01 μm, thesecond thin film layer cannot function as a lead. If the thicknessexceeds 5 μm, the lower first thin film layer is cut more than thesecond thin film layer to thereby generate gaps, moisture tends to enterthe interference and reliability deteriorates during etching.

The second thin film layer is thickened by electroless plating orelectroplating. The type of a metal formed is exemplified by copper,nickel, gold, silver, zinc, iron or the like. It is preferable to usecopper for electroplating because copper has appropriate electricalcharacteristic, is economical, has the strength and structuralresistance of the transition layer and a conductor layer to be build upin a later step mainly consists of copper. The thickness of the secondthin film layer is preferably 1 to 20 μm. If the thickness is smallerthan 1 μm, the connection reliability of the layer with the upper viahole deteriorates. If the thickness exceeds 20 μm, undercut occursduring etching and thereby gaps are generated in the interface betweenthe formed transition layer and the via hole. In some cases, the firstthin film layer may be directly plated to thicken the layer or multiplelayers may be provided.

Thereafter, an etching resist is formed with reference to thepositioning mark on the core substrate, exposure and development areperformed to expose the portions of the metal other than that of thetransition layer and etching is then performed, thereby forming atransition layer consisting of the first thin film layer, the secondthin film layer and a thickening layer on the die pad of the IC chip.

In case of forming a transition layer by a subtractive process, ametallic film is thickened by electroless plating or electroplating. Thetype of the plated member to be formed is exemplified by copper, nickel,gold, silver, zinc, iron or the like. It is preferable to use copperbecause copper has appropriate electrical characteristic and iseconomical and a buildup conductive layer to be formed later mainlyconsists of copper. The thickness is preferably in the range of 1 to 20μm. If the thickness exceeds the range, undercut occurs during etchingand gaps may be generated in the interface between the transition layerand the via hole to be formed. Thereafter, an etching resist is formed,exposure and development are performed to the portion of the metal otherthan that of the transition layer, thereby forming a transition layer onthe pad of the IC chip.

As stated above, the inventors of the present invention devisedincluding an IC chip in a package substrate by containing the IC chip ina recess formed in the core substrate and building up an interlayerresin insulating layer and a conductive circuit on the core substrate.

According to this method, a metallic film is formed on the entiresurface of the core substrate containing the IC chip so as to cover orprotect the pad of the IC chip, or, in some cases, forming a transitionlayer on the pad, thereby electrically connecting the pad to the viahole of the interlayer resin insulating layer.

However, since the metallic film is formed on the entire surface, apositioning mark formed on the IC chip is concealed and a mask on whichwirings are drawn or a laser device cannot be positioned relative to thesubstrate. Due to this, it is estimated that a positional error occursbetween the pad on the IC chip and the via hole and that electricalconnection cannot be established between the pad and the via hole.

The present invention has been made to solve the above-stated problems.It is another object of the present invention to propose a method of amultilayer printed circuit board manufacturing method capable of beingappropriately connected to an IC chip included in the multilayer printedcircuit board.

According to claim 14, a method of manufacturing a multilayer printedcircuit board having interlayer insulating layers and conductor layersrepeatedly formed on a substrate, via holes formed in the interlayerinsulatinc layers, and establishing electrical connection through thevia holes, is characterized by comprising at least the following steps(a) to (c):

(a) containing an electronic component in said substrate;

(b) forming a positioning mark on said substrate based on a positioningmark of said electronic component; and

(c) conducting working or formation based on the positioning mark ofsaid substrate.

According to claim 14, a positioning mark is formed on a substratecontaining an electronic component therein based on the positioning markof the electronic component, and working or formation is conducted basedon the positioning mark of the substrate. Due to this, it is possible toform a via hole in an interlayer resin insulating layer on the substrateso as to accurately match the position of the via hole to the positionof the electronic component.

Working in this case means the IC chip which is the electronic componentor all that formed on the substrate. For example, a transition layer onthe pad of the IC chip, a recognized character (e.g., an alphabet,number or the like), a positioning mark are included.

Also, formation in this case means all that formed on the interlayerresin insulating layer (which does not contain a reinforcement such asglass cloths) provided on the core substrate. For example, a via hole, awiring, a recognized character (e.g., an alphabet, number or the like),a positioning mark and the like are included.

According to claim 15, a method of manufacturing a multilayer printedcircuit board having interlayer insulating layers and conductor layersrepeatedly formed on a substrate, via holes formed in the interlayerinsulating layers, and establishing electrical connection through thevia holes, is characterized by comprising at least the following steps(a) to (d):

(a) containing an electronic component in said substrate;

(b) forming a positioning mark on said substrate based on a positioningmark of said electronic component by using laser;

(c) forming a metallic film on the positioning mark of said substrate;and

(d) conducting working or formation based on the positioning mark ofsaid substrate.

According to claim 15, a positioning mark is provided on a substratecontaining an electronic component therein by laser based on thepositioning mark of the electronic component, working or formation isconducted based on the positioning mark of the substrate after forming ametallic film on the positioning mark provided by laser. Due to this, itis possible to form a via hole in the interlayer insulating layer on thesubstrate so as to accurately match the position of the via hole to theposition of the electronic component. In addition, since the metallicfilm is formed on the positioning mark provided by laser, it is possibleto easily recognize the positioning mark by a reflection method and toconduct accurate positioning.

According to claim 16, a method of manufacturing a multilayer printedcircuit board having interlayer insulating layers and conductor layersrepeatedly formed on a substrate, via holes formed in the interlayerinsulating layers, and establishing electrical connection through thevia holes, is characterized by comprising at least the following steps(a) to (e):

(a) containing an electronic component in said substrate;

(b) forming a positioning mark on said substrate based on a positioningmark of said electronic component by using laser;

(c) forming a metallic film on the positioning mark of said substrate;

(d) forming the interlayer insulating layers on said substrate; and

(e) processing or forming via hole openings in said interlayer resininsulating layers based on the positioning mark of said substrate.

According to claim 16, a positioning mark is formed on a substratecontaining an electronic component therein based on the positioning markof the electronic component, working or formation is conducted based onthe positioning mark of the substrate after forming a metallic film onthe positioning mark. Due to this, it is possible to form a via hole inan interlayer insulating layer on the substrate so as to accuratelymatch the position of the via hole to the position of the electroniccomponent. In addition, the metallic film is formed on the positioningmark provided by laser. Due to this, even if an interlayer insulatinglayer is formed on the positioning mark, the positioning mark can beeasily recognized and accurate positioning can be conducted byrecognizing an image by a reflection method.

As described above, the inventor of the present invention devised astructure capable of establishing electrical connection between amultilayer printed circuit board and an IC chip without using a sealingresin, leads or bumps by providing an opening portion, a through hole ora counterbore portion in a resin insulating substrate to include anelectronic component such as an IC chip therein, building up interlayerresin insulating layers, providing a via on the pad of the IC chip byphoto-etching or laser, forming a conductor circuit serving as aconductive layer, repeatedly providing the interlayer insulating layersand the conductive layers and thereby forming the multilayer printedcircuit board.

However, since the pad of the IC chip is normally formed out of aluminumor the like, the pad is oxidized in manufacturing steps and an oxidefilm is formed on the surface of the pad. Due to this, it wasdiscovered, the oxide film formed on the surface causes an increase inthe connection resistance of the pad and, the multilayer printed circuitboard cannot be appropriately electrically connected to the IC chip. Itwas also discovered that if an oxide film remains on the die pad, theadhesiveness between the pad and the transition layer becomesinsufficient and reliability cannot be satisfied.

The present invention has been made to solve the above-stated problems.It is a still further object of the present invention to propose amultilayer printed circuit board capable of being appropriatelyelectrically connected to an IC chip without leads and a method ofmanufacturing the multilayer printed circuit board.

According to claim 17, in order to achieve the above purpose, a methodof manufacturing a multilayer printed circuit board is characterized bycomprising at least the following steps (a) to (e):

(a) containing an electronic component in said substrate;

(b) removing a film on a surface of a die pad of said electroniccomponent;

(c) forming a transition layer to be connected to a via hole of alowermost interlayer insulating layer, on said die pad;

(d) forming the interlayer insulating layers on said substrate; and

(e) forming the via holes connected to the conductor circuits and thetransition layers, in said interlayer resin insulating layers.

According to claim 17, since an IC chip is contained in a substrate, themultilayer printed circuit board can be electrically connected to the ICchip without leads. Besides, an oxide film removal process is conductedto the connection surface of the die pad of an electronic component suchas an IC chip, it is possible to reduce the electrical resistance of thedie pad and to improve electrical conductivity thereof. Further, byproving a transition layer on an IC chip portion, the IC chip portion isflattened. Due to this, the interlayer insulating layer on the IC chipis also flattened and film thickness becomes uniform. Furthermore, if avia hole on an upper layer is formed, it is possible to maintain thestability of shape. It is preferable that the film is completelyremoved.

According to claim 18, by completely removing the oxide film by one ofinverse sputtering and a plasma process, it is possible to improve theelectrical conductivity of the die pad of the IC chip.

In case of inverse sputtering, inactive gas such as argon gas is used assputtering gas and inverse sputtering is conducted to the oxide film onthe surface of the die pad, thereby completely removing the oxide film.In case of the plasma process, the substrate is put in a device in avacuum state, plasmas are discharged in oxygen or nitrogen, carbondioxide and carbon tetrafluoride to thereby remove the oxide film on thesurface of the die pad.

According to claim 19, the film removal and the formation of the lowermost layer of the transition layer are conducted under a non-oxygenatmosphere in succession. Due to this, it is possible to improve theelectrical conductivity and adhesiveness between the die pad of the ICchip and the transition layer without forming an oxide film on thesurface of the pad again.

According to claim 20, a multilayer printed circuit board havinginterlayer insulating layers and conductor layers repeatedly formed on asubstrate, via holes formed in the interlayer insulating layers, andestablishing electrical connection through the via holes, ischaracterized in that

an electronic component is included in said substrate;

a transition layer to be connected to a via hole of a lowermostinterlayer insulating layer is formed on a die pad of said electroniccomponent; and

a film on a surface of said die pad is removed.

According to claim 20, since the IC chip is contained in the substrate,the multilayer printed circuit board can be electrically connected tothe IC chip without leads. Further, since an oxide film removal processis conducted to the connection surface of the die pad of an electroniccomponent such as an IC chip, it is possible to reduce the electricalresistance of the die pad and improve the electrical conductivitythereof. Further, by providing the transition layer on the IC chipportion, the IC chif portion is flattened. Due to this, the interlayerinsulating layer on the IC chip is also flattened and film thicknessbecomes uniform. In addition, even if a via hole on the upper layer isformed, it is possible to maintain the stability of shape. It ispreferable that the film is completely removed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a process for manufacturing a multilayerprinted circuit board in the first embodiment according to the presentinvention;

FIG. 2 is a diagram showing a process for manufacturing the multilayerprinted circuit board in the first embodiment;

FIG. 3 is a diagram showing a process for manufacturing the multilayerprinted circuit board in the first embodiment;

FIG. 4 is a diagram showing a process for manufacturing the multilayerprinted circuit board in the first embodiment;

FIG. 5 is a diagram showing a process for manufacturing the multilayerprinted circuit board in the first embodiment;

FIG. 6 is a cross-sectional view of the multilayer printed circuit boardin the first embodiment;

FIG. 7(A) is a drawing showing an enlarged transition layer shown inFIG. 3(A), FIG. 7(B) is a diagram seen from B of FIG. 7(A) and FIGS.7(C), (D) and (E) are explanatory views for modifications of thetransition layer;

FIG. 8(A) is a perspective view of the multilayer printed circuit boardin the first embodiment, and FIG. 8(B) is an explanatory view for themultilayer printed circuit board which is partly enlarged;

FIG. 9(A) is a perspective view of a multilayer printed circuit board inthe first modification of the first embodiment, and FIG. 9(B) is anexplanatory view for the multilayer printed circuit board which ispartly enlarged;

FIG. 10 is a cross-sectional view of a printed circuit board in thesecond modification of the first embodiment;

FIG. 11 is a cross-sectional view of a printed circuit board in thethird modification of the first embodiment;

FIG. 12 is a cross-sectional view of a multilayer printed circuit boardin the fourth modification of the first embodiment;

FIG. 13 is a diagram showing a process for manufacturing a multilayerprinted circuit board in the second embodiment;

FIG. 14 is a diagram showing a process for manufacturing a multilayerprinted circuit board in the second embodiment;

FIG. 15 is a diagram showing a process for manufacturing a multilayerprinted circuit board in the second embodiment;

FIG. 16 is a diagram showing a process for manufacturing a multilayerprinted circuit board in the second embodiment;

FIG. 17 is a diagram showing a process for manufacturing a multilayerprinted circuit board in the second embodiment;

FIG. 18 is a cross-sectional view of the multilayer printed circuitboard in the second embodiment;

FIG. 19(A) is a plan view of a core substrate shown in FIG. 13(D), andFIG. 19(B) is a plan view of FIG. 13(E);

FIG. 20(A) is a plan view of the core substrate before a photomask filmis mounted, and FIG. 20(B) is a plan view of the core substrate in astate in which the photomask film is mounted;

FIG. 21 is a cross-sectional view of a multilayer printed circuit boardin the first modification of the second embodiment;

FIG. 22 is a diagram showing a process for manufacturing a multilayerprinted circuit board in the third embodiment;

FIG. 23 is a diagram showing a process for manufacturing the multilayerprinted circuit board in the third embodiment;

FIG. 24 is a diagram showing a process for manufacturing the multilayerprinted circuit board in the third embodiment;

FIG. 25 is a diagram showing a process for manufacturing the multilayerprinted circuit board in the third embodiment;

FIG. 26 is a cross-sectional view of the multilayer printed circuitboard in the third embodiment;

FIG. 27(A) is an enlarged, explanatory view for a die pad portion shownin FIG. 22(C), FIG. 27(B) is an enlarged, explanatory view for a die padportion shown in FIG. 23(A), and FIG. 27(C) is an enlarged, explanatoryview for a die pad portion shown in FIG. 24(A);

FIG. 28 is a cross-sectional view of a multilayer printed circuit boardin the first modification of the third embodiment;

FIGS. 29(A), (B) and (C) are drawings showing an enlarged die padportion in the first modification of the third embodiment, wherein FIG.29(A) shows a state before an oxide film removal process, FIG. 29(B)shows a state after the oxide film removal process and FIG. 29(C) showsa state after a transition layer is formed on a die pad; and

FIG. 30 is a table showing results of evaluating the multilayer printedcircuit board in the third embodiment and the multilayer printed circuitboard in a comparison example with respect to four items of 1) sectionalstate, 2) resistance measurement value, 3) sectional state after areliability test, and 4) resistance measurement value.

BEST MODES FOR WORKING THE INVENTION

The embodiments of the present invention will be described hereinafterwith reference to the drawings.

First Embodiment

First, the constitution of a multilayer printed circuit board accordingto the first embodiment of the present invention will be described withreference to FIG. 6 showing the cross-sectional view of a multilayerprinted circuit board 10.

As shown in FIG. 6, the multilayer printed circuit board 10 consists ofa core substrate 30 containing therein an IC chip 20, an interlayerresin insulating layer 50 and an interlayer resin insulating layer 150.Via holes 60 and conductor circuits 58 are formed on the interlayerresin insulating layer 50. Via holes 160 and conductor circuits 158 areformed on the interlayer resin insulating layer 150.

The IC chip 20 is covered with a passivation film 22 and die pads 24each constituting an input/output terminal are provided in the openingsof the passivation film 22. A transition layer 38 is formed on each diepad 24 made of aluminum. The transition layer 38 consists of threelayers of the first thin film layer 33, the second thin film layer 36and a thickening layer 37.

A solder resist layer 70 is provided on the interlayer resin insulatinglayer 150. BGA's 76 for connecting to an external substrate such as adaughter board or a mother board which is not shown in FIG. 6 areprovided on the conductor circuits 158 under the openings 71 of thesolder resist layer 70, respectively.

In the multilayer printed circuit board 10 in the first embodiment, theIC chip 20 is included in the core substrate 30 in advance and thetransition layer 38 is provided on each die pad 24 of the IC chip 20.Due to this, it is possible to electrically connect the IC chip to themultilayer printed circuit board (or package substrate) without usinglead members and a sealing resin. Further, since the transition layers38 are formed on the IC chip portion, the IC chip portion is flattenedand the upper interlayer insulating layer 50 is, therefore, flattened tothereby provide uniform film thickness. Further, because of thetransition layers, it is possible to maintain the stability of shapeeven if the via holes 60 provided in the upper layer are formed.

Furthermore, by providing the transition layers 38 made of copper on therespective die pads 24, it is possible to prevent resin residues on thedie pads 24 and to prevent the die pads 24 from being discolored ordissolved even after impregnating the multilayer printed circuit boardin an acid, an oxidizer or an etching solution in a later step orconducting various annealing steps. Thus, connection characteristicbetween the die pads of the IC chip and the via holes and reliabilitycan be improved. Furthermore, by interposing the transition layers 38each having a diameter of 60 μm or more on the respective die pads 24each having a diameter of about 40 μm, it is possible to ensureconnecting the via holes each having a diameter of 60 μm or more.

Next, a method of manufacturing the multilayer printed circuit boarddescribed above with reference to FIG. 6 will be described withreference to FIGS. 1 to 5.

(1) First, an insulating resin substrate (or core substrate) 30 in whichprepregs each having a core material made of glass cloths or the likeand impregnated with a resin such as epoxy are built up, is used as astarting material (see FIG. 1(A)). Next, a recess 32 for containing anIC chip is formed on one side of the core substrate 30 by counter boring(see FIG. 1(B). While the recess is provided by counter boring herein,it is also possible to from a core substrate having a containing sectionby laminating an insulating resin substrate having an opening portionand an insulating resin substrate without an opening.

(2) Then, an adhesive material 34 is applied to the recess 32 using aprinting machine. At this time, potting instead of application may beconducted. Next, an IC chip 20 is mounted on the adhesive material 34(see FIG. 1(C)).

(3) Then, the upper surface of the IC chip 20 is depressed or struck tothereby completely contain the IC chip 20 in the recess 32 (see FIG.1(D). By doing so, the core substrate 30 can be smoothed.

(4 Thereafter, the entire surface of the core substrate 30 whichcontains the IC chip 20 therein is subjected to deposition or sputteringto form the conductive, first thin film layer 33 on the entire surface(FIG. 2(A)). A metal used may be tin, chromium, titanium, nickel, zinc,cobalt, gold or copper. Nickel, chromium or titanium is more preferablebecause it is capable of suppressing the entry of moisture into aninterface, appropriate for film formation and in electricalcharacteristic. The thickness of the first thin film layer 33 ispreferably 0.001 to 2.0 μm, more preferably, 0.01 to 1.0 μm. In case ofchromium, the thickness is preferably 0.1 μm.

The die pad 24 is covered with the first thin film layer 33, therebymaking it possible to improve the adhesiveness of the transition layerand the IC chip to the interface with the die pad 24. Also, by coveringthe die pad 24 with the metal, it is possible to prevent moisture fromentering the interference, to prevent the dissolution and erosion of thedie pad and to improve reliability. Further, the first thin film layer33 allows the die pad to connect with the IC chip by a mounting methodwithout using a lead. Here, if chromium, titanium or nickel is used, itis possible to prevent the entry of moisture into the interference andto ensure high metal adhesiveness.

(5) The second thin film layer 36 is formed on the first thin film layer33 by sputtering, deposition or electroless plating (FIG. 2(B). A metalused herein may be nickel, copper, gold or silver. Copper is preferablebecause the copper has good electrical characteristic and is economicaland because a buildup conductor layer to be formed in a later stepmainly consists of copper.

The reason for providing the second thin film layer is that anelectroplating lead for forming a thickening layer to be described latercannot be provided only with the first thin film layer. The second thinfilm layer 36 is used as a lead for thickening and preferably 0.01 to 5in thickness. The thickness is more preferably 0.1 to 3 μm. The secondthin film layer having such a thickness is optimum to cover the firstthin film and serve as a lead. If the thickness is less than 0.01 μm,the second thin film layer cannot function as a lead. If the thicknessexceeds 5 μm, the first thin film layer under the second thin film layeris cut more than the second thin film layer and gaps are generatedbetween the first and second thin film layers during etching. This makesthe entry of moisture easier and deteriorates reliability.

A preferable combination of the first and second thin film layer ischromium-copper, chromium-nickel, titanium-copper, titanium-nickel orthe like. These combinations are superior to the other combinations inview of junction with a metal and electrical conductivity.

(6) Thereafter, a resist is applied, exposure and development areconducted to provide a plated resist 35 while provide an opening on theupper portion of the die pad of the IC chip, and electroplating isconducted under the following conditions to thereby provide anelectroplated film (or thickening film) 37 (FIG. 2(C)). [ElectroplatingSolution] sulfuric acid 2.24 mol/l copper sulfate 0.26 mol/l additive19.5 ml/l (Kapalacid HL manufactured by Atotech Japan)

[Electroplating Conditions] current density 1 A/dm² duration 65 minutestemperature 22 ± 2° C.

After removing the plating resist 35, the electroless-plated, secondthin film layer 36 and first thin film layer 33 under the plating resist35 are etched away, thereby forming a transition layer 38 on each of thedie pads 24 of the IC chip (FIG. 2(D)). The transition layer is formedby the plating resist in this case. Alternatively, the transition layermay be formed on each die pad by after uniformly forming anelectroless-plated film on the electroless-plated, second thin filmlayer 36, forming an etching resist, conducting exposure and developmentto expose the metal other than that of the transition layer, andconducting etching. The thickness of the electroplated film ispreferably in the range of 1 to 20 μm. If the thickness exceeds therange, undercut may possibly occur during the etching to generate gapsin the interface between the transition layer to be formed and the viahole.

(7) Next, an etching solution is sprayed onto the substrate and thesurface of the transition layer 38 is etched, thereby forming a roughsurface 38α (see FIG. 3(A)). The rough surface can be also formed byelectroless plating or an oxidization-reduction process. FIG. 7(A) is anenlarged view of the transition layer 38 shown in FIG. 3(A). FIG. 7(B)is a view seen from B of FIG. 7(A). The transition layer 38 is athree-layer structure consisting of the first thin film layer 33, thesecond thin film layer 36 and the thickening layer 37. As shown in FIG.7(A), the transition is formed to be circular. It is also possible toform the transition layer to be not circular but ellipsoidal as shown inFIG. 7(C), rectangular as shown in FIG. 7(D) or oval as shown in FIG.7(E).

(8) A thermosetting resin sheet having a thickness of 50 μm isvacuum-compression laminated onto the substrate which has gone throughthe above-stated steps at a pressure of 5 kg/cm² while raisingtemperature to 50 to 150° C., thereby providing an interlayer resininsulating layer 50 (see FIG. 3(B)). The degree of vacuum at the time ofvacuum compression is 10 mmHg.

(9) Next, using CO₂ gas laser havinq a wavelength of 10.4 μm, via holeopenings 48 each having a diameter of 80 μm are provided in theinterlayer resin insulating layer 50 under the conditions of a beamdiameter of 5 mm, a top hat mode, a pulse width of 5.0 μm, a mask holediameter of 0.5 mm and one shot (see FIG. 3(C)). Using a chromium acid,resin residues in the openings 48 are removed. By providing thetransition layer 38 made of copper on each die pad 24, it is possible toprevent resin residues on the die pad 24, thereby improving connectioncharacteristic between the die pad 24 and a via hole 60 to be describedlater and improving reliability. Furthermore, by interposing thetransition layer 38 having a diameter of 60 μm or more on the die pad 24having a diameter of about 40 μm, it is possible to ensure connectingthe via hole opening 48 having a diameter of 60 μm. While the resinresidues are removed by using a permanganic acid, a de-smear process canbe also conducted using oxygen plasma.

(10) Next, the resultant substrate is immersed in an oxidizer such as achromic acid or a permanganic acid or the like, thereby providing arough surface 50α on the interlayer resin insulating layer 50 (see FIG.3(D)). The rough surface 50α is preferably formed in the range of 0.05to 5 μm. For example, the substrate is immersed in 50 g/l of a sodiumpermanganate solution at a temperature of 60° C. for 5 to 25 minutes,thereby providing a rough surface 50α of 1 to 5 μm. Alternatively, byperforming a plasma process using SV-4540 manufactured by ULVAC JAPANLtd., the rough surface 50α can be formed on the interlayer resirinsulating layer 50. In that case, argon gas is used as inactive gas toperform a plasma process for two minutes under conditions of electricpower of 200 W, a gas pressure of 0.6 Pa and a temperature of 70° C.

(11) A metallic layer 52 is provided on the interlayer resin insulatinglayer 50 on which the rough surface 50α is formed (see FIG. 4(A)). Themetallic layer 52 is formed by electroless plating. By supplying acatalyst such as a palladium catalyst to the surface layer of theinterlayer resin insulating layer 50 in advance and immersing thesubstrate into an electroless plating solution for 5 to 60 minutes, themetallic layer 52 which is a plated film in the range of 0.1 to 5 μm isprovided. For example, the substrate was immersed in the followingsolution at a solution temperature of 34° C. for 40 minutes:[Electroless Plating Solution] NiSO₄ 0.003 mol/l tartaric acid 0.200mol/l copper sulfate 0.030 mol/l HCHO 0.050 mol/l NaOH 0.100 mol/lα,α′-bipyridyl   100 mg/l polyethylene glycol  0.10 g/l (PEG)

Alternatively, an Ni/Cu metallic layer 52 can be formed on the surfaceof the interlayer resin insulating layer 50 by exchanging internal argongas and then conducting sputtering with N and Cu as targets underconditions of an air pressure of 0.6 Pa, a temperature of 80° C., powerof 200 W and a duration of five minutes with the same device as thatused for the above-stated plasma process. At this time, the thickness ofan Ni/Cu metallic layer 52 formed is 0.2 μm. Alternatively, the metallicfilm can be formed by deposition, electrodeposition or the like insteadof sputtering. It is also possible to form a thin layer by a physicalmethod such as sputtering, deposition or electrodeposition and then toconduct electroless plating.

(12) A commercially available photosensitive dry film is bonded to thesubstrate 30 which has been subjected to the above process, a chromiumglass mask is mounted, exposure is performed at 40 mj/cm² and then adevelopment process is conducted with 0.8% sodium carbonate, therebyproviding plating resists 54 each having a thickness of 25 μm (see FIG.4(B)). Next, electroplating is conducted under the following conditionsto form an electroplated film 56 having a thickness of 18 μm. Anadditive in the electroplating solution is Kapalacid HL manufactured byAtotech Japan. [Electroplating Solution] sulfuric acid 2.24 mol/l coppersulfate 0.26 mol/l additive 19.5 mol/l (Kapalacid HL manufactured byAtotech Japan)

[Electro Plating Conditions] current density 1 A/dm² duration 65 minutestemperature 22 ± 2° C.(13) After separating and removing the plating resist 54 with 5% NaOH,the metallic layer 52 under the plating resist is dissolved and removedby etching using a mixture solution of an nitric acid and oxygenatedwater, conductor circuits 58 each consisting of the metallic layer 52and the electroplated film 56 and having a thickness of 16 μm and viaholes 60 are formed and etched by an etching solution containing acupric salt complex and an organic acid, thereby forming rough surfaces58α and 60α (see FIG. 4(C)). Alternatively, the rough surfaces can beformed by electroless plating or an oxidization-reduction process.(14) Next, the steps of (9) to (13) stated above are repeated, therebyforming an upper interlayer resin insulating layer 150 and conductorcircuits 158 (include via holes 160) (see FIG. 5(A)).(15) Then, 46.67 parts by weight of oligomer (having a molecular weightof 4000) which is obtained by forming 50% of epoxy groups of 60 parts byweight of a cresol novolac epoxy resin (manufactured by Nippon Kayaku)dissolved in diethylene glycol dimethyl ether (DMDG) into an acrylicstructure and which imparts photosensitive characteristic, 15 parts byweight of 80 wt % of a bisphenol A epoxy resin (product name: Epicoat1001 manufactured by Yuka Shell) dissolved in methylethyl keton, 1.6parts by weight of an imidazole hardening agent (product name: 2E4MZ-CNmanufactured by Shikoku Chemicals), 3 parts by weight of polyhydricacryl monomer which is a photosensitive monomer (product name: R604manufactured by Kyoei Chemical), 1.5 parts by weight of polyhydric acrylmonomer (product name: DPE6A manufactured by Kyoei Chemical), and 0.71parts by weight of a dispersing defoaming agent (product name: S-65manufactured by Sannopuko) are contained in a container, agitated andmixed to adjust mixture compositions. Then, 2.0 parts by weight ofbenzophenone (manufactured by Kanto Chemical) serving as aphotoinitiator and 0.2 parts by weight of Michler's ketone (manufacturedby Kanto Chemical) serving as a photosensitizer are added to the mixturecompositions, thereby obtaining a solder resist composition (or organicresin insulating material) adjusted to have a viscosity of 2.0 Pa·s.

Note that the viscosity is measured by using No. 4 rotor of a B-typeviscometer (DVL-B manufactured by Tokyo Keiki) when the velocity is 60rpm and using No. 3 rotor of the same when the velocity is 6 rpm.

(16) Next, the solder resist composition is applied to the substrate 30to have a thickness of 20 μm and a drying process is conducted at 70° C.for 20 minutes and 70° C. for 30 minutes. Then, a photomask film havinga pattern of the solder resist opening portions drawn thereon and athickness of 5 mm is made hermetic contact with the solder resist layer70, exposure is performed with ultraviolet rays with 1000 mj/cm² andthen a development process is performed with a DMTG solution, therebyforming openings 71 each having a land diameter of 620 μm and an openingdiameter of 460 μm (see FIG. 5(B)).

(17) Next, the substrate on which the solder resist layer (or oroanicresin insulating layer) 70 is formed, is immersed in an electrolessnickel plating solution containing nickel chloride (2.3×10⁻¹ mol/l),sodium hypophosphite (2.8×10⁻¹ mol/l), sodium citrate (1.6×10⁻¹ mol/l)and having pH=4.5 for 20 minutes, and a nickel plate layer 72 having athickness of 5 μm is formed on each opening portion 71. Then, thesubstrate is further immersed in an electroless plating solutioncontaining gold potassium cyamide (7.6×10⁻³ mol/l), ammonia chloride(1.9×10⁻¹ mol/l), sodium citrate (1.2×10⁻¹ mol/l) and sodiumhypophosphite (1.7×10⁻¹ mol/l) under the condition of 80° C. for 7.5minutes and a gold plated layer 74 having a thickness of 0.03 μm isformed on the nickel plated layer 72, thereby forming a solder pad 75 oneach conductor layer 158 (see FIG. 5(C)).

(18) Thereafter, a solder paste is printed on the opening portion 71 ofthe solder resist layer 71 and reflowed at 200° C., thereby forming aBGA's 76. As a result, it is possible to obtain a multilayer printedcircuit board 10 includinc the IC chip 20 and having the BGA's 76 (seeFIG. 6). Instead of the BGA's, PGA (conductive contact pins) may bearranged.

In the above-stated embodiment, the thermosetting resin sheet is usedfor the interlayer resin insulating layers 50 and 150. The thermosettingresin insulating sheet contains a refractory resin, soluble particles, ahardening agent and other components. The materials will now bedescribed one by one.

The epoxy resin which can be used in the thermosetting resin sheet inthe first embodiment has a structure that particles soluble in an acidor an oxidizer (to be referred to as “soluble particles” hereinafter)are dispersed in a resin which is refractory with respect to an acid oran oxidizer (to be referred to as “refractory resin” hereinafter). Theexpressions “refractory” and “soluble” are used as follows. Whenmaterials are immersed in a solution composed of the same acid or thesame oxidizer for the same time, a material of a type which is dissolvedat a relatively high dissolving rate is called a “soluble” material anda material of a type which is dissolved at a relatively slow dissolvingrate is called “refractory material” for convenience.

The soluble particles are exemplified by resin particles which aresoluble in an acid or an oxidizer (to be referred to as “soluble resinparticles” hereinafter), inorganic particles which are soluble in anacid or an oxidizer (to be referred to as “inorganic soluble particles”hereinafter), metal particles which are soluble in an acid or anoxidizer (to be referred to as “soluble metal particles” hereinafter)and the like. The foregoing soluble particles may be employed solely ortwo or more particles may be mixed.

The shape of each of the soluble particles is not limited. The shape maybe a spherical shape or a pulverized shape. It is preferable that thesoluble particles have a uniform shape. The reason for this lies in thata rough surface having uniformly rough pits and projections can beformed.

It is preferable that the mean particle size of the soluble particles is0.1 μm to 10 μm. When the particles have the diameters satisfying theforegoing range, two or more particles having different particle sizesmay be employed. That is, soluble particles having a mean particle sizeof 0.1 μm to 0.5 μm and soluble particles having a mean particle size of1 μm to 3 μm may be mixed. Thus, a more complicated rough surface can beformed. Moreover, the adhesiveness with the conductor circuit can beimproved. In the first embodiment, the particle size of the solubleparticles is the length of a longest portion of each of the solubleparticles.

The soluble resin particles are exemplified by particles constituted bya thermosetting resin or a thermoplastic resin. When the particles areimmersed in solution composed of an acid or an oxidizer, the particlesmust exhibit dissolving rate higher than that of the foregoingrefractory resin.

Specifically, the soluble resin particles are exemplified by particlesconstituted by an epoxy resin, a phenol resin, a polyimide resin, apolyphenylene resin, a polyolefin resin or a fluorine resin. Theforegoing material may be employed solely or two or more materials maybe mixed.

The soluble resin particles may exemplified by resin particlesconstituted by rubber. The rubber above is exemplified by polybutadienerubber, a variety of denatured polybutadiene rubber, such as denaturedepoxy rubber, denatured urethane rubber or denatured (meta)acrylonitrile rubber, and (meta) acrylonitrile butadiene rubbercontaining a carboxylic group. When the foregoing rubber material isemployed, the soluble resin particles can easily be dissolved in an acidor an oxidizer. That is, when the soluble resin particles are dissolvedwith an acid, dissolution is permitted with an acid other than a strongacid, and when dissolved with an oxidizer, dissolution is permitted withpermanganate which has a relatively weak oxidizing power. When chromicacid is employed, dissolution is permitted even at a low concentration.Therefore, the retention of the acid or the oxidizer on the surface ofthe resin can be prevented. When a catalyst, such as palladium chloride,is supplied after the rough surface has been formed as described later,the inhibition of supply of the catalyst and the oxidation of thecatalyst can be prevented.

The inorganic soluble particles are exemplified by particles made of atleast a material selected from a group consisting of an aluminumcompound, a calcium compound, a potassium compound, a magnesium compoundand a silicon compound.

The aluminum compound is exemplified by alumina, aluminum hydroxide andthe like. The calcium compound is exemplified by calcium carbonate,calcium hydroxide and the like. The potassium compound is exemplified bypotassium carbonate and the like. The magnesium compound is exemplifiedby magnesia, dolomite, basic magnesium carbonate and the like. Thesilicon compound is exemplified by silica, zeolite and the like. Theforegoing material may be employed solely or two or more materials maybe mixed.

The soluble metal particles are exemplified by particles constituted byat least one material selected from a group consisting of copper,nickel, iron, zinc, lead, gold, silver, aluminum, magnesium, potassiumand silicon. The soluble metal particles may have surfaces coated with aresin or the like in order to maintain insulating characteristic.

When two or more types of the soluble particles are mixed, it ispreferable that the combination of the two types of soluble particles isa combination of resin particles and inorganic particles. Since each ofthe particles has low electric conductivity, insulating characteristicwith the resin film can be maintained. Moreover, the thermal expansioncan easily be adjusted with the refractory resin. Thus, the occurrenceof a crack on the interlayer resin insulating layer constituted by theresin film can be prevented. The separation between the interlayer resininsulating layer and the conductor circuit can be prevented.

The refractory resin is not limited when the resin is able to maintainthe shape of the rough surface when the rough surface is formed on theinterlayer resin insulating layer by using an acid or an oxidizer. Forexample, the refractory resin is exemplified by a thermosetting resin, athermoplastic resin and their composite material. As an alternative tothis, the foregoing photosensitive resin of a type having photosensitivecharacteristics imparted thereto may be employed. When thephotosensitive resin is employed, exposure and development processes canbe performed to of the interlayer rein insulating layers to thereby formopenings for the via holes.

In particular, it is preferable that the resin containing athermosetting resin is employed. In the foregoing case, the shape of therough surface can be maintained against a plating solution and when avariety of heating processes are performed.

The refractory resin is exemplified by an epoxy resin, a phenol resin, aphenoxy resin, a polyimide resin, a polyphenylene resin, a polyolefinresin, a fluorine resin and the like. The foregoing material may beemployed solely or two or more types of the materials may be mixed. Athermosetting resin, a thermoplastic resin or a complex thereof may beemployed.

It is preferable that an epoxy resin having two or more epoxy groups inone molecule thereof is employed. The reason for this lies in that theforegoing rough surface can be formed. Moreover, excellent heatresistance and the like can be obtained. Thus, the concentration of astress onto the metallic layer can be prevented even under a heat cyclecondition. Thus, the occurrence of separation of the metallic layer canbe prevented.

The epoxy resin is exemplified by a cresol novolac epoxy resin, abisphenol-A epoxy resin, a bisphenol-F epoxy resin, a phenol novolacepoxy resin, an alkylphenol novolac epoxy resin, a biphenol-F epoxyresin, a naphthalene epoxy resin, a dicyclopentadiene epoxy resin, anepoxy material constituted by a condensation material of phenol and anaromatic aldehyde having a phenol hydroxyl group, triglycidylisocyanurate and alicyclic epoxy resin. The foregoing material may beemployed solely or two or more material may be mixed. Thus, excellentheat resistance can be obtained.

It is preferable that the soluble particles in the resin film used inthe first embodiment are substantially uniformly dispersed in therefractory resin. The reason for this lies in that a rough surfacehaving uniform pits and projections can be formed. When via holes andthrough holes are formed in the resin film, adhesiveness with themetallic layer of the conductor circuit can be maintained. As analternative to this, a resin film containing soluble particles in onlythe surface layer on which the rough surface is formed may be employed.Thus, the portions of the resin film except for the surface layer is notexposed to an acid or an oxidizer. Therefore, the insulatingcharacteristic between conductor circuits through the interlayer resininsulating layers can reliably be maintained.

It is preferable that the amount of the soluble particles which aredispersed in the refractory resin is 3 wt % to 40 wt % with respect tothe resin film. When the amount of mixture of the soluble particles islower than 3 wt %, the rough surface having required pits andprojections cannot be formed. When the amount is higher than 40 wt %,the deep portions of the resin film are undesirably dissolved when thesoluble particles are dissolved by using an acid or an oxidizer. Thus,the insulating layer constituted by the resin film cannot be maintained.This sometimes causes short circuit.

It is preferable that the resin film contains a hardening agent andother components as well as the refractory resin.

The hardening agent is exemplified by an imidazole hardening agent, anamino hardening agent, a guanidine hardening agent, an epoxy adduct ofeach of the foregoing hardening agents, a microcapsule of each of theforegoing hardening agents and an organic phosphine compound such astriphenylphosphine or tetraphenyl phosphonium tetraphenyl borate.

It is preferable that the content of the hardening agent is 0.05 wt % to10 wt % in the resin film. If the content is lower than 0.05 wt %, theresin film cannot sufficiently be hardened. Thus, the introduction ofthe acid and the oxidizer into the resin film occurs more frequently andthe insulating characteristic of the resin film sometimes deteriorates.When the content is higher than 10 wt %, an excessively large quantityof the hardening agent component sometimes denatures the composition ofthe resin and the reliability sometimes deteriorates.

The other components are exemplified by an inorganic compound which doesnot exert an influence on the formation of the rough surface and afiller such as a resin. The inorganic compound is exemplified by silica,alumina, dolomite and the like. The resin is exemplified by a polyimideresin, a polyacrylic resin, a polyamideimide resin, a polyphenyleneresin, a melanine resin, an olefin resin and the like. If any one of theforegoing fillers is contained, then the conformity of thermal expansioncoefficients can be established and heat resistance, chemical resistancecan be improved and the performance of the multilayer printed circuitboard can be thereby improved.

The resin film may contain a solvent. The solvent is exemplified byketone such as acetone, methyl ethyl ketone or cyclohexane, aromatichydrocarbon such as ethyl acetate, butyl acetate, cellosolve acetate,toluene or xylene. The foregoing material may be employed solely or twoor more materials may be mixed. However, the interlayer resin insulatinglayers made from the foregoing materials are dissolved and carbonated ata temperature of 350° C. or higher.

After bonding the resin film, the film is opened by laser and via holesare formed in the interlayer resin insulating layers. Thereafter, thesubstrate is immersed in an acid or an oxidizer to thereby form roughsurfaces on the interlayer resin insulating layers. The acid isexemplified by an strong acid such as a sulfuric acid, a phosphoricacid, a hydrochloric acid or a formic acid. The oxidizer is exemplifiedby a chromic acid, a mixture of chromium and a sulfuric acid,permanganate and the like. Soluble particles are dissolved or separatedusing the acid or oxidizer, thereby forming rough surfaces on theinterlayer resin insulating layers. A catalyst such as Pb is supplied tothe interlayer resin insulating layers on which the rough layers areformed, and then electroless plating is performed. Plating resistunformed regions are formed by providing a resist on the electrolessplated film and conducting exposure and development. The regions areelectroplated, the resist is separated, and the electroplated films onthe interlayer resin insulating layers are removed by etching, therebyforming via holes and conductor circuits.

FIG. 8(A) is a perspective view of the multilayer printed circuit board10 according to the first embodiment. FIG. 8(B) is an explanatory viewshowing the multilayer printed circuit board 10 which is partlyenlarged. Semiconductor bumps (ball-grid arrays) 76 are provided in ahound's tooth manner on the entire surface of the multilayer printedcircuit board 10. In the first embodiment, by forming the BGA's 76 onthe IC chip 20, it is possible to shorten the lengths of wirings fromthe IC chip 20.

[First Modification of First Embodiment]

FIG. 9(A) is a perspective view of a multilayer printed circuit board 10according to the first modification of the first embodiment. FIG. 9(B)is an explanatory view showing the multilayer printed circuit board 10which is partly enlarged in the modification. Semiconductor bumps(ball-grid arrays) 76 are provided in a hound's tooth manner on thesurface of the multilayer printed circuit board 10 in all corners exceptfor the portion on the IC chip 20. In this modification, by avoidingforming the bumps 76 on the IC chip 20, it is made advantageouslydifficult for the BGA's 76 to be thermally and electromagneticallyinfluenced by the IC chip.

[Second Modification of First Embodiment]

Next, description will be given to a multilayer printed circuit boardaccording to the second modification of the first embodiment withreference to FIG. 10. In the first embodiment stated above, descriptionhas been given to a case where the BGA's are arranged. In the secondmodification, which is almost the same as the first embodiment, themultilayer printed circuit board is constituted in a PGA mode forestablishing connection through conductive connection pins 96 as shownin FIG. 10.

[Third Modification of First Embodiment]

Next, description will be given to a multilayer printed circuit boardaccording to the third modification of the first embodiment withreference to FIG. 11.

In the first embodiment stated above, the IC chip is contained in therecess 32 provided in the core substrate 30 by counter boring. In thethird modification, by contrast, an IC chip 20 is contained in a throughhole 32 formed in the core substrate 30. In this third modification, aheat sink can be directly attached to the rear surface side of the ICchip 20, so that it is advantageous that the IC chip 20 can be cooledefficiently.

[Fourth Modification of First Embodiment]

Next, a multilayer printed circuit board in the fourth modification ofthe first embodiment will be described with reference to FIG. 12.

In the first embodiment stated above, the IC chip is contained in themultilayer printed circuit board. In the fourth modification as shown atFIG. 12, by contrast, an IC chip 20, as the first electronic component,is contained in the multilayer printed circuit board and a secondelectronic component as IC chip 120 is mounted on the surface of themultilayer printed circuit board. As the IC chip 20 included in thelayer, a cache memory having a relatively low calorific value isemployed. As the IC chip 120 mounted on the surface, a CPU forarithmetic operation is employed.

The die pads 24 of the IC chip 20 and the die pads 124 of the IC chip120 are mutually connected through transition layers 38—via holes60—conductor circuits 58—via holes 160—conductor circuit 158—BGA's 76U,respectively. On the other hand, the die pads 124 of the IC chip 120 andthe pads 92 of a daughter board 90 are mutually connected through BGA's76U—conductor circuits 158—via holes 160—conductor circuits 58—via holes60—through holes 136—via holes 60—conductor circuits 58—via holes60—conductor circuits 158—BGA's 76U, respectively.

In the fourth modification, it is possible to arrange the IC chip 120and the cache memory 20 in proximity while separately manufacturing thecache memory 20 having low yield and the IC chip 120 for the CPU, and tooperate the IC chips at high speed. In this fourth modification, byincluding an IC chip in the multilayer printed circuit board and, at thesame time, mounting an IC chip on the surface thereof, it is possible topackage electronic components such as IC chips having differentfunctions and to thereby obtain a multilayer printed circuit boardhaving greater functions.

With the structure of the first embodiment, the IC chip and the printedcircuit board can be connected to each other without using lead members.Due to this, resin sealing becomes unnecessary. Furthermore, since nodefects resulting from the lead members and sealing resin occur,connection characteristic and reliability are improved. Besides, sincethe die pads of the IC chip are directly connected to the conductivelayers of the printed circuit board, it is possible to improveelectrical characteristic.

Moreover, compared with the conventional IC chip mounting method, thewiring length from the IC chip to the substrate to the externalsubstrate can be advantageously shortened and loop inductance can beadvantageously reduced.

Second Embodiment

Next, the constitution of a multilayer printed circuit boar according tothe second embodiment of the present invention will be described withreference to FIG. 18 showing the cross-section of a multilayer printedcircuit board 210.

As shown in FIG. 18, the multilayer printed circuit board 210 consistsof a core substrate 230 containing therein an IC chip 220, an interlayerresin insulating layer 250 and an interlayer resin insulating layer 350.Via holes 260 and conductor circuits 258 are formed on the interlayerresin insulating layer 250. Via holes 360 and conductor circuits 358 areformed on the interlayer resin insulating layer 350.

The IC chip 220 is covered with a passivation film 222, and die pads 224each constituting an input/output terminal and positioning marks 223 areprovided in the respective openings of the passivation film 222. Atransition layer 238 mainly consisting of copper is formed on each diepad 224.

A solder resist layer 270 is provided on the interlayer resin insulatinglayer 350. BGA's 276 for connecting to an external substrate, such as adaughter board or a mother board which is not shown, are provided on theconductor circuits 358 under the openings 271 of the solder resist layer270, respectively.

In the multilayer printed circuit board 210 in the second embodiment,the IC chip 220 is included in the core substrate 230 in advance and thetransition layer 238 is provided on each die pad 224 of the IC chip 220.Due to this, it is possible to electrically connect the IC chip to themultilayer printed circuit board (or package substrate) without usinglead members and a sealing resin.

Furthermore, by providing the transition layers 238 made of copper onthe respective die pads 224, it is possible to prevent resin residues onthe die pads 224 and to prevent the die pads 224 from being discoloredor dissolved even after impregnating the multilayer printed circuitboard in an acid, an oxidizer or an etching solution in a later step orconducting various annealing steps.

Moreover, in manufacturing steps to be described later, positioningmarks 231 are formed on the core substrate 230 with reference to thepositioning marks 223 of the IC chip 220 and the via holes 260 areformed to conform to the positioning marks 231, respectively. Due tothis, it is possible to accurately position the via holes 260 on thepads 224 of the IC chip 220 and to ensure connecting the pads 224 to thevia holes 260, respectively.

Next, a method of manufacturing the multilayer printed circuit boarddescribed above with reference to FIG. 18 will be described withreference to FIGS. 13 to 17.

(1) First, an insulating resin substrate (or core substrate) 230, inwhich prepregs each having a core material made of glass cloths or thelike and impregnated with a resin such as epoxy are built up, is used asa starting material (see FIG. 13(A)). Next, a recess 232 for containingan IC chip is formed on one side of the core substrate 230 by counterboring (see FIG. 13(B).

(2) Then, an adhesive material 234 is applied to the recess 232 using aprinting machine. At this time, potting instead of application may beconducted. Next, an IC chip 220 is mounted on the adhesive material 234(see FIG. 13(C)).

(3) The upper surface of the IC chip 220 is depressed or struck tothereby completely contain the IC chip 220 in the recess 232 (see FIG.13(D). The plan view of the IC chip 220 and the core substrate 230 shownin FIG. 13(D) are shown in FIG. 19(A). The IC chip 220 contained in therecess 232 of the core substrate 230 is not accurately positionedrelative to the core substrate because of the working accuracy of therecess and the interposition of the adhesive material 234.

(4) The positioning marks 223 provided in the four corners of the ICchip 220 are photographed by a camera 280, and recesses 231 a areprovided in the four corners of the core substrate 230 with reference tothe positioning marks 223, respectively, by laser (FIG. 13(E)). The planview of the IC chip 220 and the core substrate 230 shown in FIG. 13(E)is shown in FIG. 19(B).

(5) Thereafter, the entire surface of the core substrate 230 whichcontains the IC chip 220 therein is subjected to deposition orsputtering, to form a conductive metallic film 233 on the entire surface(FIG. 14(A)). The metal used is formed out of one or more of tin,chromium, titanium, nickel, zinc, cobalt, gold, copper and the like. Insome cases, two or more layers may be formed out of different metals.The thickness of the metallic layer is preferably in the range of 0.001to 2.0 μm. More preferably, the thickness is 0.01 to 1.0 μm.

A plated film 236 may be formed on the metallic film 233 by electrolessplating, electroplating or a combination thereof (FIG. 14(B)). The typeof the metal used for plating is exemplified by copper, nickel, gold,silver, zinc or iron. Copper is preferably used because it hasappropriate electrical characteristic and is economical and buildupconductor layers formed in a later step mainly consist of copper. Thethickness of the plated film is preferably in the range of 0.01 to 5.0μm. If the thickness is smaller than 0.01 μm, the plated film cannot beformed on the entire surface. If the thickness exceeds 5.0 μm, itbecomes difficult to etch away the film. Besides, the positioning marksare embedded and cannot be recognized. The preferable range is 0.1 to3.0 μm. The plated film can be also formed by sputtering or deposition.

(6) Thereafter, a resist 235α is provided, a mask 239 on which patterns239 a and positioning marks 239 b corresponding to the pads 224 aredrawn is mounted (FIG. 14(C)). This mask 235 is positioned whileapplying light from above and the image of reflection light from thepositioning marks 231 is picked up by a camera 289 so that thepositioning mark through holes 231 a on the core substrate 230 side canfall in the positioning marks 239 b which are drawn to be ring-shaped.In the second embodiment, since the copper plated film 236 is formedeven on the positioning marks 231, the reflection light easily transmitsthe resist 235α and the substrate and the mask can be easily positionedrelative to each other.

(7) Plating resists 235 are formed so as to provide opening portionsabove the respective pads 224 of the IC chip by exposure and developmentand electroplated films 237 are provided by electroplating (FIG. 14(D)).After removing the plating resists 235, the electroless plated film 236and the metallic film 233 under the plating resists 235 are removed,thereby forming transition layers 238 on the pads 224 of the IC chip andforming positioning marks 231 on the recesses 231 a, respectively (FIG.14(E)).

(8) Next, an etching solution is sprayed on the substrate and thesurfaces of the transition layers 238 are etched, thereby forming roughsurfaces 238α, respectively (see FIG. 15(A)). The rough surfaces can beformed by electroless plating or an oxidization-reduction process.

(9) The same thermosetting resin sheet as that in the first embodimentis vacuum-compression laminated onto the substrate which has gonethrough the above-stated steps and an interlayer resin insulating layer250 is provided (see FIG. 15(B)).

(10) Next, the images of the positioning marks 231 are picked up by thecamera 280 while transmitting the interlayer resin insulating layer 250,thereby conducting positioning. Via hole openings 248 each having adiameter of 80 μm are provided in the interlayer resin insulating layer250 using CO₂ gas laser having a wavelength of 10.4 μm under theconditions of a beam diameter of 5 mm, a pulse width of 5.0 μseconds, amask hole diameter of 0.5 mm and one shot (see FIG. 15(C)).

(11) Next, the surface of the interlayer resin insulating layer 250 isroughened to thereby form a rough surface 250α (see FIG. 15(E)).

(12) Then, a metallic layer 252 is formed on the surface of theinterlayer resin insulating layer 250 (see FIG. 16(A)).

(13) A commercially available photosensitive dry film 254α is bonded tothe substrate 230 which has been completed with the above-stated steps,and a photomask film 253, on which patterns 253 a and positioning marks253 b corresponding to the pads are drawn, is mounted. The plan view ofthe core substrate 230 before the photomask film 253 is mounted is shownin FIG. 20(A) and a state in which the photomask film 253 is mounted isshown in FIG. 20(B). This mask 253 is positioned while light is appliedfrom above and the image of reflection light from the positioning marks231 is picked up by the camera 289 so that the positioning marks 231 atthe core substrate 230 side may fall in the positioning marks 253 bwhich are drawn to be ring-shaped. In the second embodiment, since theplated film 237 is formed on the positioning marks 231, the reflectionlight is easily transmitted by the interlayer resin insulating layer 250and the film 254α and accurate positioning can be conducted. As statedabove, the roughening process is conducted to the copper plated films237 constituting the positioning marks 231. It is also possible not toconduct the roughening process so as to increase surface reflectance orto conduct the roughening process and then conducting a surfacesmoothening process using chemicals or laser.

(14) Thereafter, exposure is performed with 100 J/cm² and a developmentprocess is conducted with 0.8% of sodium carbonate, thereby formingplating resists 254 each having a thickness of 15 μm (FIG. 16(C)).

(15) Next, electroplating is conducted under the same conditions asthose in the first embodiment to thereby form an electroplated film 256having a thickness of 15 μm (see FIG. 16(D)).

(16) After separating and removing the plating resists 254 with 5% NaOH,the metallic layer 252 under the plating resists 254 are dissolved andremoved by etching and conductor circuits 258 each consisting of themetallic layer 252, the electroplated film 256 and via holes 260 areformed and rough surfaces 258α and 260α are formed with an etchingsolution (see FIG. 17(A)).

(17) Next, the steps of (6) to (12) stated above are repeated, therebyforming an interlayer resin insulating layer 350 and conductor circuits358 (include via holes 360) further above (see FIG. 17(B)).

(18) Next, the same solder resist composition as that in the firstembodiment is applied to the substrate 230 to have a thickness of 20 μm,and a drying process is conducted. After that, exposure is conductedwith a photomask hermetically contacted with the solder resist layer270, a development process is conducted with a DMTG solution, andopening portions 270 each having a diameter of 200 μm are formed (seeFIG. 17(C)).

(19) Then, the substrate on which the solder resist layer (or organicresin insulating layer) 270 is formed is immersed in an electrolessnickel plating solution, thereby forming nickel plated layers 272 onopening portions 271, respectively. Further, the substrate is immersedin the electroless plating solution and a gold plated layer 274 having athickness of 0.03 μm is formed on each of the nickel plated layers 272,thereby forming solder pads 275 on the conductor circuits 358,respectively (see FIG. 17(D)).

(20) Thereafter, a solder paste is printed on the opening portions 271of the solder resist layer 270 and reflowed at 200° C., thereby formingBGA's 276. Thus, it is possible to obtain a multilayer printed circuitboard 210 including the IC chip 220 and having the BGA's 276 (see FIG.18). PGA's (conductive connection pins) instead of the BGA's may bearranged.

[First Modification of Second Embodiment]

Next, description will be given to a multilayer printed circuit boardaccording to the first modification of the second embodiment of thepresent invention with reference to FIG. 21.

In the second embodiment stated above, the IC chip is contained in themultilayer printed circuit board. In the first modification of thesecond embodiment, by contrast, an IC chip 220 is contained in themultilayer printed circuit board and, at the same time, an IC chip 320is mounted on the surface thereof. As for the IC chip 220 included inthe circuit board, a cache memory having a relatively low calorificvalue is employed. As for the IC chip 320 on the surface, a CPU forarithmetic operation is mounted.

In this first modification of the second embodiment, penetrating holes335 constituting the through holes 336 of a core substrate 230 areformed with reference to the positioning marks 231 of the coresubstrate.

Third Embodiment

Next, the constitution of a multilayer printed circuit board accordingto the third embodiment of the present invention will be describedhereinafter with reference to FIG. 26 showing the cross section of amultilayer printed circuit board 410.

As shown in FIG. 26, the multilayer printed circuit board 410 consistsof a core substrate 430 containing therein an IC chip 420, an interlayerresin insulating layer 450 and an interlayer resin insulating layer 550.Via holes 460 and conductor circuits 458 are formed on the interlayerresin insulating layer 450. Via holes 560 and conductor circuits 558 areformed on the interlayer resin insulating layer 550.

The IC chip 420 is covered with an IC protective film (made ofpassivation+polyimide) 422 and aluminum die pads 424 each constitutingan input/output terminal are provided in the respective openings of theIC protective film 422. An oxide film 426 is formed on each die pad 424.A transition layer 438 is formed on each die pad 424 and the oxide film426 on the surface, on which the die pad 424 and the transition layer438 contact with each other, is removed.

A solder resist layer 470 is formed on the interlayer resin insulatinglayer 550. A solder bump 476 or a conductive connection pin, which isnot shown, for connecting to an external substrate such as a daughterboard or a mother board, which is not shown, is provided on theconductor circuit 558 under each opening portion 471 of the solderresist layer 470.

In the multilayer printed circuit board 410 in this embodiment, the ICchip 420 is included in the core substrate 430 in advance and thetransition layers 420 are provided on the die pads 424 of the IC chip420, respectively. Due to this, alignment can be easily made whenforming via holes and buildup layers can be stably formed even with adie pad pitch of 150 μm or less and a pad size of 20 μm or less. If thevia holes of the interlayer resin insulating layers are formed byphotoetching with the die pads on which the transition layers are notformed and via hole diameter is larger than a die pad diameter, then thepolyimide layer serving as the protective layer on the surface of eachdie pad is dissolved and damaged during a de-smear process conducted asa via hole bottom residue removal process and a interlayer resininsulating layer surface roughening process. On the other hand, in caseof using laser, if the via hole diameter is larger than the die paddiameter, the die pads and passivation-polyimide layers (or ICprotective films) are damaged by laser. Moreover, if the pads of the ICchip are very small and the via hole diameter is larger than the die padsize, then positioning becomes quite difficult even with a photoetchingmethod or a laser method. As a result, connection errors between the diepads and the via holes frequently occur.

By providing the transition layers 438 on the respective die pads 424,by contrast, it is possible to ensure the connection of the via holes460 to the die pads 424 even with a die pad pitch of 150 μm or less anda pad size of 20 μm or less, and the connection characteristic betweenthe pads 424 and the via holes 460 and reliability are improved.Further, by interposing the transition layers each having a largerdiameter on the respective pads of the IC chip, there is no fear ofdissolving and damaging the die pads and the IC protective films(passivation-polyimide layers) even if the substrate is immersed in anacid or an etching solution in later steps such as de-smear and platingsteps or the substrate has gone through various annealing steps.

Furthermore, since the oxide film 426 formed on the die pads 424 made ofaluminum is removed on the surfaces on which the die pads 424 and thetransition layers 438 contact with one another by an oxide film removalprocess to be described later, it is possible to reduce the electricalresistances of the die pads 424 and to increase the electricalconductivity thereof.

Next, a method of manufacturing the multilayer printed circuit boarddescribed above with reference to FIG. 26 will be described withreference to FIGS. 22 to 27.

(1) First, an insulating resin substrate (or core substrate) 430 inwhich prepregs each having a core material made of glass cloths or thelike and impregnated with a resin such as epoxy are built up, is used asa starting material (see FIG. 22(A)). Next, a recess 432 for containingan IC chip is formed on one side of the core substrate 430 by counterboring (see FIG. 22(B)).

(2) Then, an adhesive material 434 is applied to the recess 432 using aprinting machine. At this time, potting instead of application may beconducted. Next, an IC chip 420 is mounted on the adhesive material 434.The IC chip 420 is covered with an IC protective film (made ofpassivation+polyimide) 422, and die pads 424 each constituting aninput/output terminal are provided in the respective openings of the ICprotective film 422. Also, the surfaces of the die pads 424 are coveredwith oxide films 426, respectively (see FIG. 22(C)). Here, anexplanatory view enlarging the die pad 424 portion of the IC chip 420 isshown in FIG. 27(A).

(3) Then, the upper surface of the IC chip 420 is depressed or struck tothereby completely contain the IC chip 420 in the recess 432 (see FIG.22(D)). It is thereby possible to flatten the core substrate 430.

(4) Next, the core substrate 430 containing therein the IC chip 420 isput in a sputtering device in a vacuum state. While argon gas which isinactive gas is used as sputtering gas, inverse sputtering is performedwith the exposed oxide films 426 on the surfaces of the die pads 424 astargets, thereby removing the exposed oxide films 426 (see FIG. 23(A)).Here, an explanatory view enlarging the die pad 424 portion of the ICchip 420 is shown in FIG. 27(B). It is thereby possible to reduce theelectric resistances of the die pads 424, to improve the electricconductivities thereof and to improve the adhesiveness thereof withcorresponding transition layers. In this case, inverse sputtering isemployed as an oxide film removal process. A plasma process instead ofthe inverse sputtering can be employed. In case of the plasma process,the substrate is put in a device in a vacuum state, plasmas aredischarged in oxygen or nitrogen, carbon dioxide and carbontetrafluoride to thereby remove the oxide films on the surfaces of thedie pads. It is also possible to process the die pad surfaces with anacid other than the plasma process and to remove the oxide films. It ispreferable to use a phosphoric acid in the oxide film removal process.The oxide films are removed herein. Even if films such as anticorrosivenitride films are formed on the die pads, it is preferable to conduct aremoval process so as to improve the electric conductivities of the diepads.

(5) Thereafter, using the same device consecutively, the entire surfaceof the core substrate 430 is sputtered with Cr and Cu as targets withoutexposing the IC chip to an oxygen atmosphere, thereby forming aconductive metallic film 433 on the entire surface (see FIG. 23(B)). Themetallic film 433 is preferably formed out of one or more layers ofmetals such as tin, chromium, titanium, nickel, zinc, cobalt, gold andsilver. The thickness of the metallic film is preferably formed to be inthe range of 0.001 to 2.0 μm. The thickness is more preferably 0.01 to1.0 μm. The thickness of a chromium layer is set so as not to generatecracks on the sputtered layer and to sufficiently hermetically contactwith a copper sputtered layer. In the third embodiment, the removal offilms and the formation of the lowermost layer (metallic layer) 433 ofeach transition layer are conducted in the same device under anon-oxygen atmosphere in succession. Due to this, it is possible toimprove the electric conductivity between the die pads 424 of the ICchip and the transition layer 438 without forming oxide films on the padsurfaces again.

A plated film 436 may be formed on the metallic film 433 by electrolessplating, electroplating or a combination thereof (see FIG. 23(C)). Thetype of the metal used for plating is exemplified by copper, nickel,gold, silver, zinc or iron. Copper is preferably used because it hasappropriate electrical characteristic and is economical and buildupconductor layers formed in a later step mainly consist of copper. Thethickness of the plated film is preferably in the range of 0.01 to 5.0μm. The thickness is more preferably 0.1 to 3 μm. The plated film can bealso formed by sputtering or deposition. The desirable combination ofthe first thin film layer and the second thin film layer ischromium-copper, chromium-nickel, titanium-copper, titanium-nickel orthe like. These combinations are superior to the other combinations injunction with metal and electric conductivity.

(6) Thereafter, a resist is applied or a photosensitive film islaminated, and plating resists 435 are provided to provide openings onthe upper portions of the pads of the IC chip 420 by exposure anddevelopment, thereby forming electroplated films 437 (see FIG. 23(D)).The thickness of the electroplated film 437 is preferably about 1 to 20μm. After removing the plating resists 435, the electroless plated film436 and the metallic film 433 under the plating resists 435 are etchedaway, thereby forming transition layers 438 on the pads 424 of the ICchip, respectively (see FIG. 24(A)). Also, an explanatory view enlargingthe die pad 424 portion of the IC chip 420 is shown in FIG. 27(C).

In this case, the transition layers 438 are formed by the platingresists. It is also possible to form the transition layers 438 on thedie pads 424 of the IC chip 420 by uniformly forming electroplated films437 on the respective electroless plated film 436, forming an etchingresist, conducting exposure and development to expose the portions ofthe metal other than those on the transition layers and conductingetching. In this case, the thickness of the electroless plated film 437is preferably in the range of 1 to 20 μm. If the thickness exceeds thatrange, undercut occurs during the etching and gaps are generated in theinterfaces between the transition layers and via holes to be formed.

(7) Next, an etching solution is sprayed on the substrate, the surfacesof the transition layers 438 are etched to thereby form rough surfaces438α on the respective surfaces (see FIG. 24(B)). It is also possible toform the rough surfaces by electroless plating or anoxidization-reduction process.

(8) A thermosetting resin sheet is vacuum-compression laminated onto thesubstrate which has gone through the above-stated steps as in the caseof the first embodiment, thereby providing an interlayer resininsulating layer 450 (see FIG. 24(C)).

(9) Next, via hole openings 448 are provided in the interlayer resininsulating layer 450 using CO₂ gas laser (see FIG. 24(D)). Thereafter,resin residues on the openings 448 may be removed using an oxidizer suchas a chromic acid or a permanganic acid. By providing the transitionlayers 438 made of copper on the die pads 424, respectively, alignmentcan be easily made at the time of forming via holes, the connection ofthe via holes onto the die pads 424 is ensured and the connectioncharacteristics between the pads and the via holes and reliability areimproved. Thus, it is possible to stably form buildup layers. Byproviding the transition layers each having a larger diameter on therespective pads of the IC chip, there is no fear of dissolving anddamaging the die pads 424 and the IC protective films(passivation-polyimide layers) 422 even if the substrate is immersed inan acid or an etching solution in later steps such as a via hole bottomresidue removal process, a de-smear process conducted as an interlayerresin insulating layer surface roughening process, a plating step andthe like or if the substrate has gone through various annealing steps.In this case, the resin residues are removed by using a permanganicacid. It is also possible to conduct a de-smear process using oxygenplasma.

(10) Next, the surface of the interlayer resin insulating layer 450 isroughened to thereby form a rough surface 450α (see FIG. 25(A)). Thisroughening step can be omitted.

(11) Next, after a palladium catalyst is supplied to the surface of theinterlayer resin insulating layer 450, the substrate is immersed in anelectroless plating solution and an electroless plated film 452 isformed on the surface of the interlayer resin insulating layer 450 (seeFIG. 25(B)).

(12) A commercially available photosensitive dry film is bonded to thesubstrate 430 which has been subjected to the above processes, achromium glass mask is mounted, exposure is performed with 40 mj/cm² andthen a development process is conducted with 0.8% sodium carbonate,thereby providing plating resists 454 each having a thickness of 25 μm.Next, electroplating is conducted under the same conditions as those inthe first embodiment, thereby forming electroplated films 456 eachhaving a thickness of 18 μm (see FIG. 25(C)).

(13) After separating and removing the plating resists 454 with 5% NaOH,the electroless plated film 452 under the plating resists is dissolvedand removed by etching, conductor circuits 458 each consisting of theelectroless plated film 452 and the electroplated film 456 and having athickness of 16 μm and via holes 460 are formed, and rough surfaces 458αand 460α are formed by an etching solution (see FIG. 25(D)). Thefollowing steps are the same as the steps (13) to (17) in the firstembodiment stated above, which description will not be given herein.

[First Modification of Third Embodiment]

Now, a multilayer printed circuit board according to the firstmodification of the third embodiment of the present invention will bedescribed with reference to FIGS. 28 and 29. FIG. 28 shows thecross-section of a multilayer printed circuit board 510 and FIG. 29 areviews showing an enlarged die pad 424 portion, where FIG. 29(A) is aview showing a state before an oxide film removal process is conducted,FIG. 29(B) is a view showing a state of the oxide film removal processand FIG. 29(C) is a view showing a state after a transition layer 438 isformed on each die pad 424.

In the third embodiment stated above, description has been given to acase where BGA's are provided. In the first modification of the thirdembodiment, which is almost the same as the third embodiment, themultilayer printed circuit board is constituted in a PGA mode forestablishing connection through conductive connection pins 496 as shownin FIG. 28.

In the manufacturing method of the first modification of the thirdembodiment, a part of the oxide film 426 of the die pad 424 is removedby conducting one of oxide film removal process from among an inversesputtering process, a plasma process and an acid process as shown inFIG. 29(B). Then, as shown in FIG. 29(C), a transition layer 438consisting of a metallic film 433, an electroless plated film 436 and anelectroplated film 437 are formed on the die pad 424. It is therebypossible to reduce the electric resistance of the die pad 426 and toimprove electrical conductivity thereof as in the case of the thirdembodiment.

Comparison Example

A multilayer printed circuit board was obtained by forming transitionlayers as in the case of the third embodiment except that film removalwas not conducted.

Test Result

The result of evaluating the multilayer printed circuit boards in thethird embodiment and in the comparison example with respect to a totalof four items of 1) sectional state, 2) resistance measurement value, 3)sectional state after reliability test, and 4) resistance measurementvalue, is shown in a table of FIG. 30.

1) Sectional State

After forming the transition layer, the layer was cut in cross sectionand whether or not an oxide film is present on the pad was observed witha microscope (×100).

2) Resistance Measurement Value

After forming the transition layer, connection resistance was measured.A numeric value measured is an average of those measured in 20 places.

3) Sectional State after Reliability Test

After forming the multilayer printed circuit board and then finishing aheat cycle test (1000 cycles with one cycle of (130° C./3 minutes)+(−60°C./3 minutes)), the multilayer printed circuit board was cut in crosssection and whether or not an oxide film was present on the pad andwhether or not the transition was separated was observed with themicroscope (×100).

4) Resistance Measurement Value after Reliability Test

After forming the multilayer printed circuit board and then finishingthe heat cycle test (1000 cycles with one cycle of (130° C./3minutes)+(−60° C./3 minutes)), connection resistance was measured. Anumeric value measured is an average of those measured in 20 places.

As shown in the table of FIG. 30, the multilayer printed circuit boardin the third embodiment had no oxide film and had a low connectionresistance value, so that no problem occurred to electrical connection.Besides, the multilayer printed circuit board in the third embodimentwas less deteriorated after the reliability test. It is noted that evenafter repeating 2000 cycles of the heat cycle test, not so a greatincrease in resistance value was observed.

In the comparison example, the oxide film remained and the connectionresistance value was high. In some cases, portions on which noelectrical connection could be established were observed. This trend wasmore conspicuous after the reliability test.

1. A multilayer printed circuit board comprising: a substrate; amultilayered structure comprising a plurality of interlayer insulatinglayers and a plurality of conductive layers each having a plurality ofconductor circuits and formed on an upper surface of the substrate, theplurality of interlayer insulating layers including a lowermostinsulating layer, the plurality of conductive layers including alowermost conductive layer formed on the lowermost insulating layer; anelectronic component having a pad and formed in the substrate; aplurality of via holes formed in the interlayer insulating layers; and atransition layer including a first thin film layer and a thick filmlayer, formed directly under a via hole formed in the lowermostinsulating layer and on the pad of the electronic component, andelectrically connecting one of the conductor circuits of the lowermostconductive layer and the pad of the electronic component through aconductive film formed in the via hole formed in the lowermostinsulating layer.
 2. A multilayer printed circuit board according toclaim 1, wherein the transition layer is formed under the lowermostinsulating layer.
 3. A multilayer printed circuit board according toclaim 1, wherein the first thin film layer and the thick film layer aremetal layers.
 4. A multilayer printed circuit board according to claim1, wherein the thick film layer is formed on the first thin film layer.5. A multilayer printed circuit board according to claim 1, wherein thetransition layer further includes a second thin film layer.
 6. Amultilayer printed circuit board according to claim 5, wherein thesecond thin film layer is formed on the first thin film layer, and thethick film layer is formed on the second thin film layer.
 7. Amultilayer printed circuit board according to claim 1, wherein the firstthin film layer is a plated metal layer.
 8. A multilayer printed circuitboard according to claim 1, wherein the first thin film layer is asputtered film layer.
 9. A multilayer printed circuit board according toclaim 1, wherein the thick film layer consists of one selected from agroup consisting of nickel, copper, gold, silver, zinc and iron.
 10. Amultilayer printed circuit board according to claim 1, wherein the firstthin film layer consists of at least one selected from a groupconsisting of tin, chromium, titanium, nickel, zinc, cobalt, gold andcopper.
 11. A multilayer printed circuit board according to claim 10,wherein the first thin film is formed as a lowermost layer of thetransition layer and has a thickness between 0.001 μm and 2.0 μm.
 12. Amultilayer printed circuit board according to claim 10, wherein thefirst thin film is formed as a lowermost layer of the transition layerand has a thickness between 0.01 μm and 1.0 μm.
 13. A multilayer printedcircuit board according to claim 1, wherein the thick film layer isformed as an uppermost layer of the transition layer and has a thicknessbetween 0.01 μm and 5.0 μm.
 14. A multilayer printed circuit boardaccording to claim 1, wherein the thick film layer is formed as anuppermost layer of the transition layer and has a thickness between 0.1μm and 3.0 μm.
 15. A multilayer printed circuit board according to claim1, wherein an upper surface of the transition layer is larger than anupper surface of the one of the pads of the electronic component.
 16. Amultilayer printed circuit board according to claim 1, wherein an uppersurface of the transition layer is larger than a bottom surface of thevia hole formed in the lowermost insulating layer.
 17. A multilayerprinted circuit board according to claim 1, wherein the transition layerhas a rough surface.
 18. A multilayer printed circuit board according toclaim 1, wherein the transition layer has a rough surface contacting theconductive film formed in the via hole formed in the lowermost layer.19. A multilayer printed circuit board according to claim 1, wherein thetransition layer has rough surfaces on side portions of the transitionlayer.
 20. A multilayer printed circuit board according to claim 1,wherein the plurality of via holes establish electrical connectionthrough the interlayer insulating layers.
 21. A multilayer printedcircuit board comprising: a substrate; a multilayered structurecomprising a plurality of interlayer insulating layers and a pluralityof conductive layers each having a plurality of conductor circuits andformed on an upper surface of the substrate in a vertical direction, theplurality of interlayer insulating layers including a lowermostinsulating layer, the plurality of conductive layers including alowermost conductive layer formed on the lowermost insulating layer; anelectronic component having a pad and formed in the substrate; aplurality of via holes formed in the interlayer insulating layers; and atransition layer being wider than the pad of the electronic component ina cross-sectional view along the vertical direction, formed directlyunder a via hole formed in the lowermost insulating layer and on the padof the electronic component, and electrically connecting one of theconductor circuits of the lowermost conductive layer and the pad of theelectronic component through a conductive film formed in the via holeformed in the lowermost insulating layer.
 22. A multilayer printedcircuit board according to claim 21, wherein an upper surface of thetransition layer is larger than an upper surface of the pad of theelectronic component.
 23. A multilayer printed circuit board accordingto claim 21, wherein an upper surface of the transition layer is largerthan a bottom surface of the via hole formed in the lowermost insulatinglayer.
 24. A multilayer printed circuit board according to claim 21,wherein the transition layer is formed under the lowermost insulatinglayer.
 25. A multilayer printed circuit board according to claim 21,wherein the transition layer comprises plural layers including at leastone thin film layer and a thick film layer.
 26. A multilayer printedcircuit board according to claim 25, wherein the thick film layer isformed on the at least one thin film layer.
 27. A multilayer printedcircuit board according to claim 25, wherein the at lease one thin filmlayer is a plated metal layer.
 28. A multilayer printed circuit boardaccording to claim 25, wherein the at least one thin film layer is asputtered film layer.
 29. A multilayer printed circuit board accordingto claim 25, wherein the thick film layer consists of one selected froma group consisting of nickel, copper, gold, silver, zinc and iron.
 30. Amultilayer printed circuit board according to claim 25, wherein the atleast one thin film layer consists of at least one selected from a groupconsisting of tin, chromium, titanium, nickel, zinc, cobalt, gold andcopper.
 31. A multilayer printed circuit board according to claim 30,wherein the at least one thin film is formed as a lowermost layer of thetransition layer and has a thickness between 0.001 μm and 2.0 μm.
 32. Amultilayer printed circuit board according to claim 30, wherein thefirst thin film is formed as a lowermost layer of the transition layerand has a thickness between 0.01 μm and 1.0 μm.
 33. A multilayer printedcircuit board according to claim 25, wherein the thick film layer isformed as an uppermost layer of the transition layer and has a thicknessbetween 0.01 μm and 5.0 μm.
 34. A multilayer printed circuit boardaccording to claim 25, wherein the thick film layer is formed as anuppermost layer of the transition layer and has a thickness between 0.1μm and 3.0 μm.
 35. A multilayer printed circuit board according to claim21, wherein the transition layer has a rough surface.
 36. A multilayerprinted circuit board according to claim 21, wherein the transitionlayer has a rough surface contacting the conductive film formed in thevia hole formed in the lowermost layer.
 37. A multilayer printed circuitboard according to claim 21, wherein the transition layer has roughsurfaces on side portions of the transition layer.
 38. A multilayerprinted circuit board according to claim 21, wherein the plurality ofvia holes establish electrical connection through the interlayerinsulating layers.